Common sense would indicate that more than likely Thug Luv was recorded first, even though Bone Thugs knew Biggie first (through recording sessions of Tha Points). Plus in Notorious Thugs, Biggie says "So-called beef with you-know-who," which was more than likely a reference to Pac.
I remember reading a Krayzie Bone interview where he said he and Bone Thugs were leaving a hotel as Pac and the Outlawz were checking in, and Pac told them that he was a fan and listened to "Tha Crossroads" a lot, probably early- to mid-1996. And then after that they clicked and worked together. And then in one of the last interviews with Pac, he names people who were going to be recording on Makaveli Records or something, and Bone Thugs was one of the names mentioned. I think this interview was NOT on the Last Interview CD, but it might be on the Thug Immortal DVD during the main feature.